LTC3554-3_15 Datasheet, PDF (27/36 Pages) Linear Technology – Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators

LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPERATION
press must start in the PUP1, PUP2 or PON state, but
can end in any state. If a valid HRST event is present in
PON, PDN2 or POFF, then the state machine will transition
to the PDN1 state and subsequently transition to the HR
state one second later.
Debounced Pushbutton Output (PBSTAT)
In the PON, PUP1, and PUP2 states, the PBSTAT open-drain
output pin outputs a debounced version of the ON push-
button signal. ON must be held low for at least 50ms for
the pushbutton interface to recognize it and cause PBSTAT
to go low. PBSTAT goes high impedance when ON goes
high, except the logic enforces a minimum pulse width on
PBSTAT. Once it goes low, it stays low for at least 50ms.
In the HR, POFF, PDN1, and PDN2 states, PBSTAT remains
high impedance regardless of the state of ON.
Power-Up Via Pushbutton Press
Figure 7 shows the LTC3554 powering up through ap-
plication of the external pushbutton. For this example the
pushbutton circuitry starts in the POFF or HR state with a
battery connected and both bucks disabled. Pushbutton
application (ON low) for 400ms transitions the pushbutton
circuitry into the PUP state and powers up buck1 followed
by buck2 (except LTC3554-3). In the LTC3554-3, buck1
and buck2 power up at the same time. If either PWR_ON
is low or goes low after the 5 second period the corre-
sponding buck(s) will be shut down. In the above example
PWR_ON2 is low at the end of the 5 second period and
therefore buck2 is disabled at the end of the 5 second
period. PGOOD is asserted once all enabled bucks are
within 8% of their regulation voltage for 230ms.
1
BAT
0
1
V_BUS
0
1
ON (PB)
0
1
PBSTAT
0
1
BUCK1*
0
400ms
1
BUCK2
0
1
PGOOD
0
1
PWR_ON1
0
230ms
5s
1
PWR_ON2
0
STATE
POFF/HR
PUP2/PUP1
*BUCK1 AND BUCK2 FOR THE LTC3554-3
PON
3554 TD01
Figure 7. Power-Up Via Pushbutton Press
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